Grid for electron discharge devices



Aug. 1, 1950 M. ARDll'l ETAL 2,516,841

7 GRID FOR ELECTRON DISCHARGE DEVICES Filed Jan. 16, 1946 4 Sheets-Sheet 1 COPE ME 724L INVENTORS Mfll/R/CE JED/77 VINCENT J. DESfl/YT/J Aug. .1, 1950 M. ARDITI ETAL GRID FOR ELECTRON DISCHARGE DEVICES 4 Sheets-Sheet 2 Filed Jan. 16, 1946 GAIO POWEA lA/Pl/T ATTO Aug. 1, 1950 M. ARDITI arm.

pan: FOR ELECTRON DISCHARGE DEVICES 4 Sheets-Sheet 3 Fi led Jan. 16, 1946 v .M. v nwwfikit 3 EEWQEN wmutktu PLATE you/reef ATTOHVEY 1950 M. ARDITI :rAL

GRID FOR summon DISCHARGE nmvxcss.

4 Sheets-Sheet 4 Filed Jan; 16, 1946 TU8E#2 ,ciow P097250 Gem INPUT 70 11 /0 //r WHTTJ INVENTORS MHMF/CE APO/77 V/NCE/VT J. Mam/r15 Patented Aug. 1, 1950 i UNITED? ;JS"TAfI :E"S:.:-. PATIENT o Ffic 2,516,841,. w GRID FOR'ELECTRQN DIs'cHARoEnEvmEs Maurice :Arditi,:New'ork,-:;N. Y., and Vincent J; De Santis-,3- Chatham,N:J.-,:assignors:toEederal- Telephone and. Radio. ,Corporation; rNew York; i N. Y., a corporation .ofqDelawai'e I 7 Application January 16,1946; SeriatlfNo-Gflfifill 3Claims: (Gl.i2501'l7.):o?-: :4

This invention relates to gridsfor eiectron w'vThe gridbremetalis preferably molybdenum discharge devices. Grid structuresin the anode-1 r :or=tungstenor anyworkablehigh melting metal cathode space of rad-i0 tubes which operate at -which will no't sag or warp at red or even white ultra-high and micro-wave frequencies usually operating temperatures: Molybdenum is a demust dissipate disproportionately large amounts? tfi'isirable metal forth'egrid and spiral supports beof heat energy-J Theeg-ridiis"heatedi-by inductionp cause of its malleability. The' surface of the core by electron a'ndion bombardmentg and. by radiametal, according to-the characteristic feature of tion from the" cathoda-and-becauSe of the-finee'ithis inveiition't-dndas shown in Fig. 3, is a layer wire construction ofthe g rid,*the"grid is first of carbide Orr-boron (BsC); Finely powdered Y to reach the limiting temperature 'aof itheftubezt' l0 boron carbide is 'made to adhere tothe core pref- Even at temperatures below which the grid nor-s1. BIabIy by si-n-teringfl thedepth of the coating being mally operates, i-there amayi-be considerable prisuificient to 'substantially conceal the underlying mary emission fromi -thei.wirestand-a:consequent w score, and=-the grain size of'the' powder being such reductionin tube input impedancemli'inally, g'as wasto give an even, smooth non-porous and someevolved and metais evaporated from::.=.the..grid lfi what carbonizewappearance to the grid." One will poison "and1%.reduce -cathode emission. 17 3'? suitable grain-size for use is found to be 800 mesh.

An object oflthis invention is-improvedwgridsw: wElectrondischarge devices having a grid with for electron discharge devices: 1,1 .v-irc-x a boron carbide surface have been found to oper i A more specific objectnof. this inve'ntionwis ami .ate throughouta normal life at rated power grid of metak havingia:high-smelting pointnandfli) 1evels,;wvith low grid emission, and n'ormalcathhaving a fsuflacewithblack body. characteristics, TOde emissibn-i -Goodresults were obtained with low primary and; secondary -zemissiongi low vapon wmedium and high powe'rshort-wave tubes of the pressureyiandrsgood electrical.conductivity-rmw. type show-min Fig.- 1* in which the grid-cathode The characteristicfeatures rof this invention -spacing was-about .076 inc'ha'n'd .005 inch as well are definediinothe 'appendedeclaims anda--pre- .25 a s;interm'ediate limitsa The" emission from-the ferred embodimentvisrdescribed. int-the following flcathode with-" an oxide coating indicated no specification and shown in the accompanying drawings, inrwhichtz-x i 1 I a normally close grid-cathode spacing. In addi- Fig. 1 is :arrve'rtical sectional view- -of: one elecetion to the low emission from the grid and-the tron discharge device having'thesnoyelegrid oi;.iideomplete absxice .of poisoning efiects on the" this inventiong gm i v ,cathode,the bbron carbide coating onthe: grid Fig.2is atypical gridstructuregw it has good 'conductivity for high frequency cur-- Fig. 3 is ia -;sectionoofthe. novels grid' and -pa it... .rents. When operatedat fiofl megacycles; the Q Figs. 4.5:;andfi arecuryesshowing comparative -of a resonant cavit'y madesbetween such a coated H operational;oharacteristicsvof grids ltreate mac 1 ;grid and an anode mas -about-1200, as compared cording toour invention. 0-,: with mas-ear piire'molybdenumand 1700 for pure The discharge device of Fig.1 is of the medium tantalum' 'grid. power, highafrequency. type inwhich the grid is The above=deseribed grid wasmade by spraysubject toc'onsiderable heating. The anode l, ing a wetrmixture of thepowdered 'boron' carbide *n'v cathode 2 and grid 3 .are.cylindri @1zfl d.coaxial 40 on the wires ofhai prefabricated gridistructureit and are sealed in envelope 4, the lead-in for the One specific mixture ionnd to'igive g'oodxresultszt r: if anode beingiisealed: atthe lowerisendrorithe smwas prepared by ba'll 'milling commercial boron envelope, well removed from the grid and :cathode'. .i carbide. An -inei liquidibirider veh cle for supportsfi and B respectively. eThe desirable-propthe p d r onsisting of 26-100: of py erties of the novel grid here described are obtained 45 nitrocellulose dissolved in 243 cc. of amyl acetate when the cathode is the conventional, barium-mamas 11 Edi" 11 fi i '-p d f being m d in the" strontiuni oxidevcoated. core. wsoneiisin'lfile grid liquid o u aipaiintiof s consistency structure showniin Fig. 2 .comprises'samuppema. i to. spray well from an air-operated-ispray igun. tral s rtin member landea spaced supmi; illniform coatingsronltheiagrids were obtained by porting bandor colla'rfl to...which.are:s'ecured b, 91.mbuntingthe grids rotating fix and a terspot welding a pluralitynygf tfine vertical grid nately spraying-anddrying with infra-rect.radia-. wires 9. A spiral of fine wire"lll' is wouridaround tion. The passes @weretrepeated until about 10.2. the cylinder formed by wires 9 andfiecured to the milligrams of coating pensquare centimeterswere: wires, for Xamplepby-welding-to ake the struc depositedi whereupori the coating was-bakedunderx 1.. I 5 an inira red -iighte The coated -gridsiwere thenizz.

tendencyto drop below-normal despite the-'abnother grid coating which was also satiscry was prepared as follows:

vto 25 cc. of tetraethyl orthosilicate is added 3. of material composed mainly of ethyl alcoienatured with methyl alcohol, ethyl acetate, 1yl isolintylketane and aviation gasoline.

. 4 emission in tubes having the treated grids. It is seen that the cathode emission is higher for these tubes with the treated grids than it is for the tubes using the untreated grids, again the filament voltages being 7, 6.3 and 6 respectively. In Fig. 6 is shown curve 2| illustrating the grid emission-in jmilliamperes plotted against i added material is commercially available er the trade name of Synasol. This mixis stirred until it is uniform. Then to this mm is added 5 cc. of .3% hydrochloric acid the solution is stirred until hydrolysis is com- 2d and allowed to stand three hours before 27 grams of boron carbide (800 mesh) are into a mortar and 40.5 cc. of the binder mixdescribed above is put in at the rate of about 0. at a time. Between each addition of the er the mixture is ground with a pestle until orm, care being taken to see that the final ;ure is free of all lumps. l grids to be coated with this mixture should be vapor degreased in trichloroethylene and heated in an atmosphere of hydrogen at degrees C. for fifteen minutes. When these ations are complete the grids are not touched bare hands. are is. then sprayed on the surface of the using as fine a spray as possible. ioilitate the deposition of a smooth uniform inathe grids should be rotated at about 100 M. during application of the coating. Sufiit coating should be sprayed onto the surface isure complete coverage. It was found that it 3 milligrams per square centimeter of ed surface is the optimum weight of coating. ter the grid has been sprayed the coating be dried by placing it about four inches L an infra-red radiating lamp, the grid being ly turned. The coated grid may then be nbled in the tube. If desired the grids may .rst vacuum fired before they are assembled. 1e final tube. 1 1e vacuum firing may be carried out in the lope in which the grid is finally mounted the other electrodes, or the firing may be e in a separate envelope or bell-jar'before ."nbly, high frequency induction being the practical source of heating energy. irning now to Fig. 4, the operating character-- a of the tube prepared in'accordance with invention may be observed. This figure s grid emission in microamperes plotted in iii-logarithmic scale against the grid power t in watts. Curves H and I2 illustrate the emission obtained from pure molybdenum after twenty one and thirty two hours ation respectively, while curves I3 and M- r grid emission curves on the same scale for treated with boron carbides. This shows grid emission is reduced to an extremely value while the untreated grids have ex- .ely high emission. I

lrning now to Fig. 5, a comparison is shown een the cathode emission and plate voltage ubes having treated and untreated grids. In intreated grids as shown in curves l5, l6 and llament voltages of '7, 6.3 and 6 volts respecy, are shown. At [8, l9 and are shown similar. respective curves, for... the .p'athode,

The prepared boron carbide In order grid input in watts for a tube having a tungsten carbide treated grid. Curve 22 shows a similar grid emission curve in a common standard in lowgrid emission, that is, .a gold plated grid. Curves 23' and '24 illustrate boron carbide treated grids, curve 24 showing the operation after ageing forone hundred and forty hours. For all grid inputs the boron carbide grids are shown to be far superior to the tungsten carbide treated grids. -For all grid inputs above ten the boron carbide grid i shown to be superior to the gold plated grid. Furthermore, after one hundred and forty hours of ageing with a power input to the cathodeas high as 25 watts the grid emission from the boron carbide treated grid is even lower than it was initially as clearly demonstrated in curve 24. 1

The grid of this invention will emit negligible quantities of electrons even at high operating temperatures 1 and will not adversely affect cathode emission. The grid has good conductivity for high frequency current and is simple and easy to manufacture.

We claim:

' 1. An electron discharge device comprising a cathode having an' emissive coating of mixed oxides of barium and strontium, and a control electrode, said control electrode comprising a core of molybdenum bearing an adherent, external coating of a mixture of boron carbide and an inert binder on said core.

2. An electron discharge device comprising a cathode having an emissive coating of mixed oxides of barium and strontium, and a control electrode, said'control electrode comprising a core of molybdenum, a layer of sintered particles of boron carbide and the core material on said core, and a layer of a mixture of boron carbide and an inert binder on said layer of sintered particles.

3. An electron discharge device comprising a cathode having an emitting surface of bariumstrontium oxides and a control electrode, said control electrode comprising a core of molybdenum, a layer of sintered particles of boron carbide and the core material on said core, and a smooth, external layer of a mixture ofboron carbide and'an inertbinderon said layer of sintered particles.

iviAunrcn ARDITI.

VINCENT J. DE SANTIS. REFERENCES CITED The following references are of record in the file of this patent:

1 UNITED' seams PATENTS 

